Much of the oil produced in the United States and throughout the world is by pumping wells. Normally when an oil well is first drilled into a subterranean producing formation sufficient gas pressure in the formation exists to force the oil to the earth's surface. However, as the formation pressure diminishes, it is necessary to install a pump. The most common type of oil well pump utilizes a string of sucker rods which extend from the earth's surface to the pump at the bottom of the well. At the earth's surface, a pumping unit is employed to impart reciprocal motion to the sucker rods. At the upper end of the sucker rod, a stuffing box is utilized to permit reciprocation of the sucker rod, but nevertheless confines the produced petroleum to a collecting pipe. In order to seal around the sucker rods, the upper end is connected with a rod having a smooth exterior surface which is customarily referred as a "polish rod". Thus, the pumping unit imparts reciprocal energy to the polish rod which is connected at the lower end to the sucker rod, and the sucker rods impart this reciprocal energy to the pump in the well to raise fluid in the well to the earth's surface.
Many wells require that the pump be located extremely deep in the earth, and the location of pumps more than one mile deep is not uncommon. This requires a long vertical string of sucker rods and requires the pumping unit to exert substantial lifting forces to raise the sucker rods, the pump at the bottom of the well, and the column of fluid which is being raised to the earth's surface on each upward stroke of the pumping unit. Because of the length of the sucker rod string, standing force waves can develop in the rod string. In addition, the contact of the rod string with the inside of well tubing and the opening and closing of pump valves results in an uneven load as the string of sucker rods and pumps are lifted vertically on each reciprocal stroke of the pumping unit. This uneven load can result in high load peaks, and when coupled directly to the pumping unit results in shock loads which are delivered to the various components making up the pumping unit. A typical pumping unit includes a prime mover and gears connecting the rotary motion from the prime mover to a crank arm which in turn is connected to a walking beam. These shock loads can cause accelerated wear and damage to the pumping unit gear train, bearings, the prime mover, and so forth. The present invention is directed toward a means of providing a method of interconnecting the polish rod of a well with the pumping unit so that the lifting force provided by the pumping unit to the polish rod is transmitted in a way such as to diminish transient shock leads from the polish rod to the pumping unit and thereby provide a more even load on the pumping unit.
It is therefore an object of this invention to provide a device for interconnecting the lifting load from a pumping unit to a polish rod which decreases the transmission of shock loads between these two components.
A specific object of the invention is to provide a shock absorber for use on an oil well pumping unit and polish rod including elastomeric rings for absorbing the shock load between the two, and wherein the rings include openings therethrough arranged so that air is trapped in the opening and so that as the elastomeric members are compressed by increasing loads, the air trapped in the openings is compressed providing an air cushion in addition to the elastomeric cushion to achieve an improved shock absorber.
These objects, as well as other and more specific objects of the invention, will be fulfilled in the apparatus described in the attached specification and illustrated in the drawings.